This invention relates to a dry shaving apparatus
A dry shaving apparatus of the type initially referred to is known from U.S. Pat. No. 2,339,677. The shaving head formed of a shaving head frame and an outer cutter and an inner cutter is arranged on an upper housing surface of a housing for reciprocating movement transverse to the direction of movement of an inner cutter driven to oscillate in the longitudinal direction. To transmit the driving motion to the inner cutter on the one hand and to the shaving head on the other hand, a double eccentric device is provided on the rotary shaft of an electric motor fixedly disposed in the housing. The masses comprised of shaving head, inner cutter and double eccentric device which are driven for reciprocating movement in different directions by driving elements produce excessive vibrations perceivable to the user because of the development of loud noise in addition to causing handling discomfort.
A dry shaving apparatus of the type referred to in the foregoing is also known from DE 1 711 665. In all embodiments of this known printed specification, the drive element of the electric drive mechanism is linked, likewise through transmission elements such as a gear mechanism or a double eccentric device or a double-armed lever, to both the inner cutter and the shaving head equipped with an outer cutter, in order to set the inner cutter and, in addition, the complete shaving head in motion. Considering the masses to be set in motion by the electric drive mechanism of this specification, which include the transmission elements and the inner cutter and, in addition, the complete shaving head assembly comprised of shaving head frame, outer cutter and inner cutter, the electric motor is required to deliver an increased power output which needs to be taken into account correspondingly in the design of the dry shaving apparatus. The masses needing to be accelerated in different directions due to the oscillations and to be decelerated as well, transmit oscillation couples to the housing of the dry shaving apparatus through the electric drive mechanism secured to the housing. This effect is noticeable on the housing in the form of unpleasant vibrations and loud noise under load.
From DE 3 631 120 A1 it is known to use eccentric balance weights to dynamically balance in a dry shaving apparatus the masses such as eccentric device, oscillatory bridge structure with coupling element as well as inner cutter, which are driven to reciprocate by an electric drive mechanism, that is, an electric motor, in order to suppress undesired vibrations. These balance weights which are associated with the electric drive mechanism necessarily require an increased power output of the electric drive mechanism, resulting directly in increased cost of the electric drive mechanism and, in cases where a dry shaving apparatus is equipped with rechargeable storage cells, in an increased consumption of stored energy and hence a reduced number of shaves per charge of the storage cells.
It is an object of the present invention to improve upon a dry shaving apparatus of the type identified in the foregoing.
According to the present invention, this object is accomplished in a dry shaving apparatus of the type initially referred to by the features indicated in the main claim.
This approach of the present invention affords a plurality of advantages. When the electric drive mechanism is started, the electric drive mechanism is excited to oscillate in opposition to the direction of movement of one or, where applicable, several cutting elements by the masses set in motion by the drive element and also by the friction occurring between the cutting elements provided. Because according to the present invention the electric drive mechanism is mounted for oscillation, this oscillating excitation, which in the hitherto conventional, standard rigid fastening of an electric drive mechanism to the shaver housing is transmitted from the electric drive mechanism to the shaver housing where it consequently produces unpleasant vibration and loud noise, rather than being transmitted to the housing, remains initially with the electric drive mechanism, causing it to oscillate about its axis. The electric drive mechanism hence follows the oscillatory motions forced upon it without significant effect on the housing of the dry shaving apparatus. This approach effects first a material reduction of housing vibration and noise under load that is derivable therefrom. According to the present invention, these oscillatory motions of the electric drive mechanism are utilized advantageously to set the shaving head of the dry shaving apparatus in oscillation. The oscillation of the shaving head and hence the cutting element fixed in the shaving head produces a relative motion between the skin and the cutting element. In consequence, tips of hair that are located in close proximity to the cutting element and threadedly engage therebetween only sparingly in the absence of oscillation are then in a position to penetrate the cutting openings of the cutting element in major quantities. In addition, the oscillation of the shaving head operates to lengthen the effective hair entrance openings in the cutting element in the direction of oscillation. The threaded hair is entrained by the cutting element configured as inner cutter, the cut being performed against the edge of the hair entrance opening in the cutting element configured as outer cutter. According to the present invention, the outer cutter moves against the inner cutter, thereby shortening the length of displacement of a hair that has penetrated the hair entrance opening during the cutting operation, whereby the hair is cut to a shorter length. The cutting performance of the dry shaving apparatus is thus significantly improved. Moreover, on account of the high oscillation frequency of the shaving head, a reduced sliding friction of the cutting element becomes effective on the skin.
An essential advantage of the present invention resides in that the oscillating excitation originating from the movable masses, rather than being transmitted to the housing of the dry shaving apparatus as is known from DE-GM 1 711 665, is transmitted, via the oscillatory mounting of the electric drive mechanism, to the movable shaving head. Hence the energy of the oscillating excitation is routed from a location in the housing where disturbing effects occur to a location where this energy can be put to use in advantageous manner. For lack of linkage of its drive element with the oscillatory shaving head, the electric drive mechanism is thus not required to supply driving power to this shaving head.
In a further configuration of this invention, provision is made for at least the shaving head and the electric drive mechanism to be mounted for oscillation as an oscillating mass about a common axis of oscillation.
To compute the position of the axis of oscillation for the electric drive mechanism in the housing, allowance must be made for the fact that the oscillating mass is formed by incorporating the oscillating mass of the electric drive mechanism as well as all components adapted to be set in oscillation by the oscillatory motions of the electric drive mechanism, such components including, for example, the shaving head, support arms for the shaving head and/or bearing cage for the electric drive mechanism and/or an oscillatory bridge structure for an additional cutting unit or by fitting additional oscillating masses.
In a preferred embodiment of the present invention, the electric drive mechanism is mounted for oscillation about an axis of oscillation.
A preferred embodiment of the present invention is characterized in that the shaving head is mounted for oscillation in the housing by means of at least one oscillating element.
In a preferred embodiment of the present invention, the oscillating element is formed by support arms having joints.
In another embodiment of the present invention, the oscillating element is formed by a housing portion.
A substantial improvement of the cutting performance of the cutting elements and an appreciable reduction in vibration of the housing of the dry shaving apparatus are obtainable by arranging the axis of oscillation so as to extend through the center of impact of the oscillating mass. The center of impact of the oscillating mass is the location about which the motor would oscillate if a drive unitxe2x80x94comprised of electric drive mechanism and driven elementsxe2x80x94operating at rated speed were able to oscillate freely. At this location the bearing forces to be exerted for the oscillating mass, which in this case is the drive unit, reach their minimum, causing undesired housing vibration to be reduced to a minimum.
According to another embodiment of the present invention, the axis of oscillation is provided at a distance to the center of impact of the oscillating mass. With such an approach it is possible to vary, for example, the extent of the oscillation amplitude of the electric drive mechanism and hence of the shaving head linked thereto in simple manner.
In a preferred embodiment of the present invention, the shaving head is drivable by the oscillatory motions of the electric drive mechanism in the directions of movement A and B of the drivable cutting element. In a further aspect of this embodiment, provision is made for the shaving head to be driven by the electric drive mechanism so as to oscillate in opposition to the reciprocating movements of the cutting element. This approach results in an improved cutting performance by reducing the hair displacement travel in the hair entrance openings of the outer cutter.
According to the present invention, the cutting performance of the cutting elements is improved by providing for different oscillation amplitudes for the shaving head and the movable cutting element. This approach ensures, for example, an optimum configuration and adaptation of movable cutting elements relative to stationary cutting elements, incorporating the wide variety of geometries of hair entrance openings in cutting elements operating as outer cutter. The invention further affords a substantial advantage in that the oscillation amplitudes of the shaving head and/or the cutting element are variable. The respective oscillation amplitudes can be varied, for example, by varying the masses adapted to be set in oscillation, or by relocating the axis of oscillation away from the center of impact of the oscillating mass.
In a preferred embodiment of the present invention, provision is made for the oscillation amplitude to be determinable by the cutting element and for the oscillation amplitude of the shaving head to be adjustable thereto. This approach ensures an optimum relative adjustment of cooperating cutting elements. Tests performed on a dry shaving apparatus of the present invention revealed that the reciprocating travel of the shaving head in each direction of movement A and B should be provided in a range from 0.05 mm to 1 mm. In a preferred embodiment of the present invention, the reciprocating travel of the shaving head should be in a range from 0.15 mm to 0.5 mm. An optimum magnitude of the reciprocating travel of the shaving head for a particular type of dry shaving apparatus should be determined on a case-by-case basis, taking into account the respective configuration of cooperating cutting elements, in particular the hair entrance opening geometries.
In another aspect of the present invention, the electric drive mechanism is mounted for oscillation about the axis of oscillation by means of pivot bearings. These pivot bearings operate to largely decouple the electric drive mechanism from the unavoidable housing vibration in addition to ensuring at the same time that this vibration energy is utilized to advantage to cause an oscillatory motion of the shaving head. By means of these low-friction pivot bearings the electric drive mechanism is mounted for oscillation in the housing of the dry shaving apparatus, such that it follows the oscillation forced upon the electric drive mechanism without appreciable reaction on the housing.
An embodiment of the present invention affording ease and economy of manufacture is characterized in that the pivot bearing is provided on at least one support element of the housing and on a housing portion of the electric drive mechanism. In another advantageous embodiment of the present invention, provision is made for the housing portion of the electric drive mechanism to be securable in a bearing cage.
According to an embodiment of the present invention, provision is made for the axis of oscillation to be aligned in a direction transverse to the directions of movement A and B of the cutting element. In a preferred embodiment of the present invention, the pivot bearing for the electric drive mechanism is configured as a conical bearing.
To make sure that the shaving head performs an oscillatory motion in the directions of movement A and B, a preferred embodiment of the present invention makes provision for at least one support arm for the shaving head. In a further aspect of this embodiment, at least two joints are provided on the support arm. For the purpose of transmitting the oscillatory motion forced upon the electric drive mechanism to the shaving head, this embodiment makes provision for at least one support arm to be adapted to be linked to the electric drive mechanism through an oscillating element having joints. These joints may be formed, for example, by joint boltsxe2x80x94not shownxe2x80x94slidably received in bores. According to an embodiment affording low cost manufacture of joints, at least one joint is configured as a film hinge.
In an advantageous embodiment of the present invention, provision is made for the support arm to be linked through one joint to at least one support element, and through another joint to the shaving head frame of the shaving head, such as to be capable of oscillating in the directions of movement A and B. This embodiment corresponds to a mechanism referred to as a four-bar mechanism. In another embodiment of the present invention, the joint for the support arm is provided in the housing at the housing end opposite the shaving head. This embodiment makes use of the available length of the housing of the dry shaving apparatus to accommodate the length of the support arm, whereby the vertical component derivable from the oscillatory motion is reduced in magnitude to a minimum, so that a nearly linear oscillatory motion is accomplished in the directions of movement A and B of the shaving head.
A further very advantageous embodiment of the present invention is characterized in that the support arm is linked for oscillation to at least one support element at the one end and to a supporting frame carrying the shaving head at the other end. In this embodiment, the supporting frame is adapted to be linked to the electric drive mechanism directly, and this through a housing portion of the electric drive mechanism or through a bearing cage encompassing it. In a further aspect of this embodiment, provision is made for the electric drive mechanism to be adapted to be linked to the supporting frame through a housing portion and an engaging device. A simple and low cost embodiment for the transmission of motion from the electric drive mechanism or a housing portion of the electric drive mechanism to the supporting frame is characterized in that the engaging device is formed of a slot and a pin engageable in said slot.
In a further embodiment of the present invention, provision is made for the drive element of the electric drive mechanism to be adapted to be linked through an oscillatory bridge structure to a cutting element of the shaving head. In a still further embodiment of the present invention, the drive element of the electric drive mechanism is adapted to be linked through at least one eccentric device to a cutting element of the shaving head. Another embodiment of the present invention is characterized in that the drive element of the electric drive mechanism is adapted to be linked through an eccentric device configured as a double eccentric device to cutting elements of different configurations. Cutting elements of different configurations are understood to mean the cutting elements of a short-hair cutterxe2x80x94see FIG. 1xe2x80x94and the cutting elements of a long-hair trimmer as well. The long-hair trimmer may be provided on or in the housing of the dry shaving apparatus or in a shaving head in known manner (not shown).
In a further aspect of the present invention, provision is made for the eccentric member of a double eccentric device to be adapted to be linked to a cutting element of a long-hair trimmer through an oscillatory bridge structure. In a preferred embodiment of the present invention, the electric drive mechanism is configured as a direct-current motor having a drive element provided for rotation. An alternative embodiment is characterized in that the electric drive mechanism is configured as a rocking armature motor having an oscillatory drive element.
In another embodiment of the present invention, provision is made for the electric drive mechanism and the shaving head to be held in a mid-position by means of a spring element. In a further aspect of this embodiment, the spring elements bear with one end against the electric drive mechanism and with their other end against the housing.